
/* Copyright 1998 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

#include "ares_setup.h"

#ifdef HAVE_STRINGS_H
#include <strings.h>
#endif

#include "ares.h"
#include "ares_private.h"

struct search_query {
    /* Arguments passed to ares_search */
    ares_channel channel;
    char* name; /* copied into an allocated buffer */
    int dnsclass;
    int type;
    ares_callback callback;
    void* arg;

    int status_as_is; /* error status from trying as-is */
    int next_domain; /* next search domain to try */
    int trying_as_is; /* current query is for name as-is */
    int timeouts; /* number of timeouts we saw for this request */
    int ever_got_nodata; /* did we ever get ARES_ENODATA along the way? */
};

static void search_callback(void* arg, int status, int timeouts,
    unsigned char* abuf, int alen);
static void end_squery(struct search_query* squery, int status,
    unsigned char* abuf, int alen);
static int cat_domain(const char* name, const char* domain, char** s);
STATIC_TESTABLE int single_domain(ares_channel channel, const char* name, char** s);

void ares_search(ares_channel channel, const char* name, int dnsclass,
    int type, ares_callback callback, void* arg)
{
    struct search_query* squery;
    char* s;
    const char* p;
    int status, ndots;

    /* If name only yields one domain to search, then we don't have
   * to keep extra state, so just do an ares_query().
   */
    status = single_domain(channel, name, &s);
    if (status != ARES_SUCCESS) {
        callback(arg, status, 0, NULL, 0);
        return;
    }
    if (s) {
        ares_query(channel, s, dnsclass, type, callback, arg);
        ares_free(s);
        return;
    }

    /* Allocate a search_query structure to hold the state necessary for
   * doing multiple lookups.
   */
    squery = ares_malloc(sizeof(struct search_query));
    if (!squery) {
        callback(arg, ARES_ENOMEM, 0, NULL, 0);
        return;
    }
    squery->channel = channel;
    squery->name = ares_strdup(name);
    if (!squery->name) {
        ares_free(squery);
        callback(arg, ARES_ENOMEM, 0, NULL, 0);
        return;
    }
    squery->dnsclass = dnsclass;
    squery->type = type;
    squery->status_as_is = -1;
    squery->callback = callback;
    squery->arg = arg;
    squery->timeouts = 0;
    squery->ever_got_nodata = 0;

    /* Count the number of dots in name. */
    ndots = 0;
    for (p = name; *p; p++) {
        if (*p == '.')
            ndots++;
    }

    /* If ndots is at least the channel ndots threshold (usually 1),
   * then we try the name as-is first.  Otherwise, we try the name
   * as-is last.
   */
    if (ndots >= channel->ndots) {
        /* Try the name as-is first. */
        squery->next_domain = 0;
        squery->trying_as_is = 1;
        ares_query(channel, name, dnsclass, type, search_callback, squery);
    } else {
        /* Try the name as-is last; start with the first search domain. */
        squery->next_domain = 1;
        squery->trying_as_is = 0;
        status = cat_domain(name, channel->domains[0], &s);
        if (status == ARES_SUCCESS) {
            ares_query(channel, s, dnsclass, type, search_callback, squery);
            ares_free(s);
        } else {
            /* failed, free the malloc()ed memory */
            ares_free(squery->name);
            ares_free(squery);
            callback(arg, status, 0, NULL, 0);
        }
    }
}

static void search_callback(void* arg, int status, int timeouts,
    unsigned char* abuf, int alen)
{
    struct search_query* squery = (struct search_query*)arg;
    ares_channel channel = squery->channel;
    char* s;

    squery->timeouts += timeouts;

    /* Stop searching unless we got a non-fatal error. */
    if (status != ARES_ENODATA && status != ARES_ESERVFAIL
        && status != ARES_ENOTFOUND)
        end_squery(squery, status, abuf, alen);
    else {
        /* Save the status if we were trying as-is. */
        if (squery->trying_as_is)
            squery->status_as_is = status;

        /*
       * If we ever get ARES_ENODATA along the way, record that; if the search
       * should run to the very end and we got at least one ARES_ENODATA,
       * then callers like ares_gethostbyname() may want to try a T_A search
       * even if the last domain we queried for T_AAAA resource records
       * returned ARES_ENOTFOUND.
       */
        if (status == ARES_ENODATA)
            squery->ever_got_nodata = 1;

        if (squery->next_domain < channel->ndomains) {
            /* Try the next domain. */
            status = cat_domain(squery->name,
                channel->domains[squery->next_domain], &s);
            if (status != ARES_SUCCESS)
                end_squery(squery, status, NULL, 0);
            else {
                squery->trying_as_is = 0;
                squery->next_domain++;
                ares_query(channel, s, squery->dnsclass, squery->type,
                    search_callback, squery);
                ares_free(s);
            }
        } else if (squery->status_as_is == -1) {
            /* Try the name as-is at the end. */
            squery->trying_as_is = 1;
            ares_query(channel, squery->name, squery->dnsclass, squery->type,
                search_callback, squery);
        } else {
            if (squery->status_as_is == ARES_ENOTFOUND && squery->ever_got_nodata) {
                end_squery(squery, ARES_ENODATA, NULL, 0);
            } else
                end_squery(squery, squery->status_as_is, NULL, 0);
        }
    }
}

static void end_squery(struct search_query* squery, int status,
    unsigned char* abuf, int alen)
{
    squery->callback(squery->arg, status, squery->timeouts, abuf, alen);
    ares_free(squery->name);
    ares_free(squery);
}

/* Concatenate two domains. */
static int cat_domain(const char* name, const char* domain, char** s)
{
    size_t nlen = strlen(name);
    size_t dlen = strlen(domain);

    *s = ares_malloc(nlen + 1 + dlen + 1);
    if (!*s)
        return ARES_ENOMEM;
    memcpy(*s, name, nlen);
    (*s)[nlen] = '.';
    memcpy(*s + nlen + 1, domain, dlen);
    (*s)[nlen + 1 + dlen] = 0;
    return ARES_SUCCESS;
}

/* Determine if this name only yields one query.  If it does, set *s to
 * the string we should query, in an allocated buffer.  If not, set *s
 * to NULL.
 */
STATIC_TESTABLE int single_domain(ares_channel channel, const char* name, char** s)
{
    size_t len = strlen(name);
    const char* hostaliases;
    FILE* fp;
    char* line = NULL;
    int status;
    size_t linesize;
    const char *p, *q;
    int error;

    /* If the name contains a trailing dot, then the single query is the name
   * sans the trailing dot.
   */
    if ((len > 0) && (name[len - 1] == '.')) {
        *s = ares_strdup(name);
        return (*s) ? ARES_SUCCESS : ARES_ENOMEM;
    }

    if (!(channel->flags & ARES_FLAG_NOALIASES) && !strchr(name, '.')) {
        /* The name might be a host alias. */
        hostaliases = getenv("HOSTALIASES");
        if (hostaliases) {
            fp = fopen(hostaliases, "r");
            if (fp) {
                while ((status = ares__read_line(fp, &line, &linesize))
                    == ARES_SUCCESS) {
                    if (strncasecmp(line, name, len) != 0 || !ISSPACE(line[len]))
                        continue;
                    p = line + len;
                    while (ISSPACE(*p))
                        p++;
                    if (*p) {
                        q = p + 1;
                        while (*q && !ISSPACE(*q))
                            q++;
                        *s = ares_malloc(q - p + 1);
                        if (*s) {
                            memcpy(*s, p, q - p);
                            (*s)[q - p] = 0;
                        }
                        ares_free(line);
                        fclose(fp);
                        return (*s) ? ARES_SUCCESS : ARES_ENOMEM;
                    }
                }
                ares_free(line);
                fclose(fp);
                if (status != ARES_SUCCESS && status != ARES_EOF)
                    return status;
            } else {
                error = ERRNO;
                switch (error) {
                case ENOENT:
                case ESRCH:
                    break;
                default:
                    DEBUGF(fprintf(stderr, "fopen() failed with error: %d %s\n",
                        error, strerror(error)));
                    DEBUGF(fprintf(stderr, "Error opening file: %s\n",
                        hostaliases));
                    *s = NULL;
                    return ARES_EFILE;
                }
            }
        }
    }

    if (channel->flags & ARES_FLAG_NOSEARCH || channel->ndomains == 0) {
        /* No domain search to do; just try the name as-is. */
        *s = ares_strdup(name);
        return (*s) ? ARES_SUCCESS : ARES_ENOMEM;
    }

    *s = NULL;
    return ARES_SUCCESS;
}
